Press forming method

ABSTRACT

A press forming method is disclosed, wherein press forming can be effected at high speed while maintaining the horizontal state of a slide plate in press-forming a work-piece by a press machine. A press machine is used in which the slide plate is pressed by a plurality of drive sources using servo-motors for driving. The speed of one of the plurality of drive sources is set to a target speed for production forming for the drive source, and by using a function that shows a delay in terms of a speed of the drive source and a load thereon and also using a load separately found, the respective speeds of the drive sources are found so as to eliminate the delay between the drive sources. Trial forming is repeated on the basis of the thus-found speed to derive conditions that enable press-forming at high speed while maintaining the horizontal state of the slide plate.

TECHNICAL FIELD

The invention relates to a press forming method in which a slide plateis maintained to be horizontal during press forming, using a pressmachine that drives a slide plate or a pressing plate by a plurality ofdrive sources, e.g. servo-motors, to press-form.

BACKGROUND ART

A press machine for press-forming a work-piece has a structure which hasa fixed plate, a slide plate opposite to the fixed plate, a fixed diedisposed on the fixed plate and a movable die disposed on the slideplate facing the fixed plate to open and close the movable die againstthe fixed die by moving the slide plate relatively to the fixed plate.In a small press machine, there is a single drive source provided in acenter of a slide plate. Using a large slide plate, the single drivesource disposed in a center of the slide plate cannot uniformly pressthe slide plate. Therefore, using a plurality of drive sources to causea uniform pressing force on a slide plate, each of the plurality ofdrive sources presses a respective engaging portion disposed on theslide plate to form a press plane on the slide plate. As the pluralityof drive sources, there have two, four or six ones, for example, beenused.

When a slide plate is descending against a fixed plate to close amovable die against a fixed die and to increase a pressing force,magnitudes of loads working to the movable die through a plate to beformed are changing and working positions of the loads on the movabledie are, also, varying. The variations of the magnitudes and the workingpositions of the loads cause imbalance on load working on the slideplate. A distance from a working position of a load on the slide plateto a drive source, also, is varied. Then, imbalance in load momentsacting to the drive sources is caused.

When servo-motors are used for drive sources of a press machine,revolutions of the servo-motors are delayed by loads working to thedrive sources. So, since a drive source subjected to a large load ismore delayed in proceeding than a drive source subjected to a smallload, a slide plate is caused to incline relatively to a fixed plate.The inclination of the slide plate causes a die to incline and often tobe injured. When the inclination of the slide plate is small, the die isnot injured but may reduce accuracy in press-forming a work-piece.

As a countermeasure, an inclination of a slide plate has been correctedby detecting/measuring the inclination of the slide plate during aprogress of the press-forming and adjusting a driving signal supplied toeach of the drive sources to reduce/eliminate the inclination of theslide plate. Such a feed-back control can prevent the slide plate frominclining during press-forming.

However, when a slide plate inclination is prevented duringpress-forming by the feed-back control, a cycle of press forming takes along time. In a press-forming of a work piece, it is usual that a samekind of work-pieces is repeatedly formed to produce a large number ofwork-pieces. If a cycle of press-forming takes a long time, there is aproblem that a production of a large number of work-pieces takes anextremely long time.

DISCLOSURE OF THE INVENTION

An object of the invention, therefore, is to provide a press-formingmethod that enables press-forming at a high forming speed suitable formass production, while maintaining a slide plate horizontal.

The invention has been made on the basis of discovery that a delay of aslide plate on the way of press-forming is shown by a function of a loadworking on the slide plate from a work-piece.

A press forming method of the invention comprises the steps of:

-   providing a press machine comprising    -   a fixed plate,    -   a slide plate disposed to face the fixed plate and movable        relatively to the fixed plate and    -   a plurality of drive sources each having a servo-motor for        driving the slide plate and pressing each of a plurality of        engaging portions positioned on the slide plate to press        horizontally the slide plate,-   measuring a load working on each of the plurality of drive sources    at each of descending displacements of the slide plate, while the    slide plate is displaced to press-form a work-piece,-   applying the load at each of the descending displacements and a    target speed for production forming for one (hereinafter referred to    as “reference drive source”) of the plurality of drive sources at    each of the descending displacements to a function that shows a    delay of a drive source from an instructed displacement in terms of    a speed of the drive source and a load working on the drive source,    thereby calculating a speed (hereinafter referred to as    “compensation speed”) for each of the plurality of drive sources to    eliminate a delay for each of the plurality of drive sources from    the reference drive source,-   driving each of the plurality of drive sources at the compensation    speed to press-form a work-piece in a trial forming,-   measuring a delay of each of the plurality of drive sources during    the trial forming,-   until delays of other drive sources from the reference drive source    become not more than a predetermined value, repeating correction of    the compensation speed, the trial forming and the measurement of the    delay during the trial forming, and-   when the delays of the other drive sources from the reference drive    source become not more than the predetermined value, press-forming    work-pieces at corrected respective speeds of the plurality of drive    sources in a production forming.

In the description above, it is desirable that the reference drivesource is among the plurality of drive sources a drive source on whichthe smallest load works at each of the descending displacements.

In the press-forming method of the invention, it is also desirable thatthe compensation speed (Vn) for a drive source (n) is expressed asVf+ΔVn, in which Vf is a target speed for the reference drive source andΔVn is a speed increment for the reference drive source from the targetspeed (Vf) for the compensation speed (Vn) calculated by using afunction that shows a delay of a drive source in terms of a speed of thedrive source (n) and a load working on the drive source (n), and thatthe trial forming is performed by driving each of the plurality of drivesources at a speed of Vf+50 to 90% of the speed increment calculatedabove.

In the press-forming method described above of the invention, a loadworking on each of the plurality of drive sources may be measured in atrial forming of a work-piece, or obtained by simulation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of a press machine which can be used for theinvention;

FIG. 2 is a plan view showing the press machine shown in FIG. 1 with anupper support plate being partially removed;

FIG. 3 is a block diagram showing a control system of the press machinewhich can be used for the invention;

FIG. 4 is a flow chart showing a press forming method according to anexample of the invention and

FIG. 5 is a graph showing an example of relationship of displacement anddelay.

BEST MODE FOR CARRYING OUT OF THE INVENTION

Referring to FIGS. 1 and 2 first, an example of a press machine whichcan be used for the invention will be described. FIG. 1 is a front viewof the press machine, and FIG. 2 is a plan view of the press machine. InFIG. 2, the press machine is shown with an upper support plate partiallyremoved. The press machine has a lower support base 10 fixed on a floorsurface, and has an upper support plate 30 by supporting columns 20 madeupright on the lower support base. A slide plate 40 capable ofreciprocating along the supporting columns 20 is provided between thelower support base 10 and the upper support plate 30, and a formingspace exists between the slide plate and the lower support base. In thisforming space, a fixed die (lower die) 81 for press-forming is mountedon the lower support base, while a movable die (upper die) 82corresponding to the fixed die is mounted on an undersurface of theslide plate, and for example, a plate to be formed is placed betweenthese dies and press-formed.

Four of the combinations of servo-motors and decelerating mechanisms aremounted on the upper support plate 30 as drive sources 60 a, 60 b, 60 cand 60 d. Drive shafts 61 a, 61 b, 61 c and 61 d that extend in adownward direction from each of the drive sources through through-holesprovided in the upper support plate 30 are engaged with each of engagingportions 62 a, 62 b, 62 c and 62 d on the slide plate 40. For example, aball screw is attached to each of the drive shafts so as to convertrevolution into an up and down movement, and the slide plate is moved upand down by revolution of the serve-motors. Driving mechanisms areconstructed by the drive sources, the drive shafts and the engagingportions.

It is preferable that these drive sources are positioned so that pushingpressure onto the slide plate by a plurality of drive sources 60 a, 60b, 60 c and 60 d horizontally presses the slide surface and isdistributed uniformly on the slide plate. It is preferable that thesedrive sources generate the pushing pressure of equal magnitude to eachother, namely, generate equal output force.

As is apparent from the plan view of FIG. 2, each of the engagingportions 62 a, 62 b, 62 c and 62 d is provided in a forming area of theforming space. Displacement measuring devices 50 a, 50 b, 50 c and 50 dare provided near the respective engaging portions 62 a, 62 b, 62 c and62 d. As each of the displacement measuring devices 50 a, 50 b, 50 c and50 d, a device having a magnetic scale 51 provided with magneticcalibration markings and a magnetic sensor 52 such as a magnetic headprovided to face the magnetic scale with a small clearance therebetweencan be used. On moving the magnetic sensor 52 relatively to the fixedmagnetic scale 51, its absolute position, displacement speed and thelike can be measured. Such a displacement measuring device is well knownto those skilled in the art as a linear magnetic encoder, and therefore,further explanation win be omitted. As the displacement measuringdevice, a device which measures a position by light or a sonic wave canbe also used. The magnetic scale 51 of each of the displacementmeasuring devices 50 a, 50 b, 50 c and 50 d is mounted to a referenceplate 70, and the magnetic sensors 52 of the displacement measuringdevices are supported by supporting columns 53 mounted to the respectiveengaging portions 62 a, 62 b, 62 c and 62 d. Here, the reference plate70 is maintained at the same position irrespective of the position ofthe slide plate 40. Therefore, when the slide plate 40 is driven by thedrive sources 60 a, 60 b, 60 c and 60 d, displacement of each of theengaging portions can be measured by the displacement measuring devices50 a, 50 b, 50 c and 50 d.

The reference plate 70 that is provided under the upper support plate 30with a clearance with the upper support plate in FIG. 1, is laid betweenthe supporting columns 20 and fixed, and has a through-hole 71 having asufficient clearance with the drive shafts at a portion where each ofthe drive shafts 61 a, 61 b, 61 c and 61 d is passed, so that anydeformation of the drive shafts and the slide plate does not influencethe reference plate.

At each of the engaging portions 62 a, 62 b, 62 c and 62 d, there is aload measuring device 55 a, 55 b, 55 c and 55 d provided between each ofthe engaging portions and the slide plate 40 to measure a load workingon the slide plate at each of the engaging portions.

A control system block diagram of the press machine is illustrated inFIG. 3. Before press-forming, for example, a name of a product to beformed, speed of each of the drive sources and the like are inputted toa control device 92 from an input device 91 in advance. The controldevice 92 has a CPU, to transmit driving signals to the drive sources 60a, 60 b, 60 c and 60 d through an interface 94 from the control device92 to drive each of the drive sources and perform press-forming.Displacement signals of the slide plate are transmitted to the controldevice 92 from the displacement measuring devices 50 a, 50 b, 50 c and50 d. And the load applied on the slide plate is measured by each of theload measuring devices 55 a, 55 b, 55 c and 55 d and the data about theload is sent to the control device 92.

In FIG. 4, a press forming method according to an example of theinvention is shown by a flow chart. In step 1 of the flow chart, a trialforming of a work-piece is performed. During the trial forming, a loadapplied on each of the drive sources 60 a, 60 b, 60 c and 60 d engagedto the slide plate 40 is measured to obtain loads at each of descendingdisplacements of the slide plate.

That is, a driving signal is supplied to each of the drive sources 60 a,60 b, 60 c and 60 d to rotate the servo-motors and to descend the slideplate 40. When a die starts to contact a forming plate to be formed, theloads working on the slide plate are varied to make the slide plate 40inclined. Descending progresses of the drive sources can be monitored bythe descending displacements of the slide plate measured by thedisplacement measuring devices 50 a, 50 b, 50 c and 50 d providedadjacent to the drive sources, and a progress of a drive source that isdelayed in progress can be hastened. Displacement at a portion of theslide plate at which each of the drive sources is provided is made sameto make the slide plate horizontal and descended. Repeating these steps,the slide plate is descended until the end of the press-forming and thenafter the press-forming, the slide plate is returned to the originalplace to complete a cycle of the trial forming.

At each of appropriate time periods or each of appropriate displacementsduring the press-forming, or every time when an inclination of the slideplate exceeds a certain value or when a load difference exceeds acertain value, descending displacements of the slide plate and loadsworking on each of the drive sources are measured by the load measuringdevices 55 a, 55 b, 55 c and 55 d and the measured data are stored in amemory device 93 to prepare a table of displacements with loads in thememory device. Assume that, when the slide plate is descended, a movabledie contacts a forming plate at displacement l₀ and respective loadsworking on the drive sources 60 a, 60 b, 60 c and 60 d are P_(a1),P_(b1), P_(c1) and P_(d1) when the slide plate reaches displacement l₁.Further, the respective loads become P_(a2), P_(b2), P_(c2) and P_(d2)when the slide plate comes to displacement l₂. And, the respective loadsare P_(am), P_(bm), P_(cm) and P_(dm) when the press forming furtherprogresses and the slide plate is at displacement l_(m). The table ofthese displacements with the loads is shown in TABLE 1.

TABLE 1 LOAD DRIVE DRIVE DRIVE DRIVE DISPLACE- SOURCE SOURCE SOURCESOURCE MENT 60a 60b 60c 60d l₁ P_(a1) P_(b1) P_(c1) P_(d1) l₂ P_(a2)P_(b2) P_(c2) P_(d2) . . . . . . . . . . . . . . . l_(m) P_(am) P_(bm)P_(cm) P_(dm) . . . . . . . . . . . . . . .

The loads working on each of the drive sources change in magnitude ofthe loads and position of the loads like, for example, at displacementl₁, P_(a1) is the largest and P_(d1) is the smallest, while P_(b2) isthe largest and P_(d2) is the smallest at displacement l₂. It is assumedthat P_(am)<P_(dm)<P_(bm)<P_(cm) at displacement l_(m).

In this example, respective loads working on the drive sources aremeasured in a trial forming, but the loads at each of displacements maybe obtained by simulation.

As shown in FIG. 5, by the loads P_(am), P_(bm), P_(cm) and P_(dm)working on the drive sources at displacement l_(m), the drive source 60c is most delayed in descending displacement among the drive sources andthe delay is δc, while the drive source 60 a is least delayed indescending displacement and the delay is δa. In FIG. 5, the verticalaxis is an instructed displacement and the horizontal axis is a delay δof actual displacement from the instructed displacement of the slideplate near each of the drive sources. At instructed displacementl_(m−1), there is no relative delay among the drive sources. Therelative delay becomes largest at l_(m) and returns to zero at l_(m+1).Since the load on the drive source 60 a is smallest among the loads onrespective drive sources at displacement l_(m) and the delay indescending displacement of the drive source 60 a is smallest, the drivesource is set to a reference drive source.

Since the delay δa is the smallest among the largest delays δa, δb, δcand δd of the drive sources in displacement period of l_(m−1) tol_(m+1), δa is set to δmin. A target speed of the drive source 60 a(reference drive source) that the smallest load is applied on in thedisplacement period of l_(m−1) to l_(m+1) is set to Vf. The target speedis a speed for a production forming of a drive source. In step 2, speedsVn (n:b, c and d) of each of the drive sources n are obtained toequalize delays of the drive sources with the delay δmin of the drivesource 60 a, by using loads P_(am), P_(bm), P_(cm) and P_(dm) working onthe drive sources 60 a, 60 b, 60 c and 60 d and the target speed Vf ofthe drive source 60 a.

Since a delay δ of a portion, on which a load P works, from aninstructed displacement is in general expressed by a function of itsspeed V and a load P, δ=f(V, P). When the drive source 60 a is driven ata speed Vf, a speed Vn of a drive source n that has the same delay δn asthe delay δmin of the drive source 60 a is calculated as follows.

Namely, Vn (n=b, c, d) is obtained from f(Vn, P_(nm))=f(Vf, P_(am)),since δn−δmin=0.

Using speeds of the drive sources obtained, a work-piece is press-formedfor trial forming in step 3. The speed Vn obtained above for each of thedrive sources n may be expressed as a sum of a target speed Vf of thereference drive source and a speed increment ΔVn. It is preferable thata speed of each of the drive sources is set to 50% to 90% of theobtained increment ΔVn in the trial forming in step 3. This is becausethe calculated speed Vn is reduced since the speed Vn calculated aboveis applied during the period of displacement l_(m−1) to displacementl_(m+1), assuming that there is a uniform delay during the period.Further more, since a speed increment is obtained by calculation hereand there might be a risk in applying the calculated speed increment toa real press machine, it is better to use a less speed increment thanthat to avoid the risk. Although a drive source of the smallest load isused as the reference drive source in the explanation, another drivesource may be a reference drive source. When another drive source isused as a reference drive source, an increment ΔVn might be negative andthat should be taken care.

During the trial forming in step 3, delays of the drive sources aremeasured and, in step 4, the largest value δn of a delay for each of thedrive sources n is obtained and the smallest value among the largestvalues is set to δmin. In step 5, the largest delay δn for each of thedrive sources n is compared with the smallest value δmin among thelargest values δn's and, if the difference between on and δmin is morethan a predetermined value α, the compensation increment ΔVn used beforeis corrected in step 6, and steps 3, 4 and 5 are repeated. Although itis necessary that the value a for comparison of the difference betweenδn and δmin is such an inclination that dies is not broken (for example,less than 100 μm), it is preferable that the criteria is less than 10 μmfor increase of accuracy of products, specifically about 3 μm.

If the difference between the largest delay δn for each of the drivesources n and the smallest delay value δmin among the largest delays isless than or equal to the predetermined value a in the comparison ofstep 5, the flow goes to step 7 and a production forming of a work-pieceis performed, using speeds of the drive sources obtained in a previouscycle.

INDUSTRIAL APPLICABILITY

When work-pieces are press-formed while the horizontal state of theslide plate is maintained by a feedback control, much time is taken forone cycle of the press-forming. However, if the production forming isperformed by setting the speed of each of the drive sources so that thehorizontal state of the slide plate can be maintained as in theinvention, high descending speed of the slide plate can be selected inthe production forming, and therefore, during press-forming, the formingcan be performed at high forming speed suitable for production formingwhile the slide plate is maintained horizontal.

1. A press forming method comprising the steps of: providing a pressmachine comprising a fixed plate, a slide plate disposed to face thefixed plate and movable relatively to the fixed plate and a plurality ofdrive sources each having a servo-motor for driving the slide plate andpressing each of a plurality of engaging portions positioned on theslide plate to press horizontally the slide plate, measuring a loadworking on each of the plurality of drive sources at each of descendingdisplacements of the slide plate, while the slide plate is displaced topress-form a work-piece, applying the load at each of the descendingdisplacements and a target speed for production forming for one(hereinafter referred to as “reference drive source”) of the pluralityof drive sources at each of the descending displacements to a functionthat shows a delay of a drive source from an instructed displacement interms of a speed of the drive source and a load working on the drivesource, thereby calculating a speed (hereinafter referred to as“compensation speed”) for each of the plurality of drive sources toeliminate a delay for each of the plurality of drive sources from thereference drive source, driving each of the plurality of drive sourcesat the compensation speed to press-form a work-piece in a trial forming,measuring a delay of each of the plurality of drive sources during thetrial forming, until delays of other drive sources from the referencedrive source become not more than a predetermined value, repeatingcorrection of the compensation speed, the trial forming and themeasurement of the delay during the trial forming, and when the delaysof the other drive sources from the reference drive source become notmore than the predetermined value, press-forming work-pieces atcorrected respective speeds of the plurality of drive sources in aproduction forming.
 2. A press forming method as set forth in claim 1,wherein the reference drive source is among the plurality of drivesources a drive source on which the smallest load works at each of thedescending displacements.
 3. A press forming method as set forth inclaim 1, wherein the compensation speed (Vn) for a drive source (n) isexpressed as Vf+ΔVn, in which Vf is a target speed for the referencedrive source and ΔVn is a speed increment for the reference drive sourcefrom the target speed (Vf) for the compensation speed (Vn) calculated byusing a function that shows a delay of a drive source in terms of aspeed of the drive source (n) and a load working on the drive source(n), and the trial forming is performed by driving each of the pluralityof drive sources at a speed of Vf+50 to 90% of the speed incrementcalculated above.
 4. A press forming method as set forth in claim 2,wherein the compensation speed (Vn) for a drive source (n) is expressedas Vf+ΔVn, in which Vf is a target speed for the reference drive sourceand ΔVn is a speed increment for the reference drive source from thetarget speed (Vf) for the compensation speed (Vn) calculated by using afunction that shows a delay of a drive source in terms of a speed of thedrive source (n) and a load working on the drive source (n), and thetrial forming is performed by driving each of the plurality of drivesources at a speed of Vf+50 to 90% of the speed increment calculatedabove.